Everything below is a mix of rumours/facts gathered using the devs twitter (now shut down because of the leaks) and the industrious sleuthing of the denizens of NeoGaf, who are also responsible for the gorgeous header image up top:

RUMOURED CHARACTER LIST (SOME ARE CONFIRMED/WITH PROOF)3rd Party (12 Characters)

Chell (Confirmed)

John Marston (Based on a dev image saying “Marston. J” in characters)

James Bond (Confirmed)

Isaac Clarke

Captain Price

The Prince (Katamari)

Altair

Paul Phoenix

Rayman

Lightning

Old Snake

Agent 47 (NO info suggesting this yet)

1st Party (26 Characters including double teams)

Clank + Daxter Team

Parappa + Lammy Team

Bentley + George Team (Sly Cooper) (Unknown if true)

Spike + Ape Team (NO info suggesting this yet)

Rico (Killzone) (Confirmed)

Radec (Killzone) (Confirmed)

Nathan Drake (Confirmed)

Sir Daniel Fortesque

Toro (Japanese Sony Mascot)

Chimera Grunt

Cole Mcgrath (Confirmed)

Noby Noby Boy

Sackboy (Confirmed)

Ratchet

Jak

Sweet Tooth

Kratos

Buzz

Unnamed Starhawk Character (Confirmed)

Gabe Logan

Fat Princess (Confirmed)

Modnation Racer Mod

Cameo appearances / attacks from:

Wipeout Ships

Warhawk planes

SOCOM attack squad

Zombies from Medieval including Zarrok

Quark and Nefarious bursting in

Metal Gear Rex

Timesplitters Characters

Sully and Elena cameo

Level in creation from LBP

Buzz questions popping up

Atlas and P-body + GlaDOS cropping up on portal level

SOTC/Ico/The Guardian remix Stage

That’s all fine and dandy but will it have Kevin Butler? I don’t care if he is the announcer; I want this man in the game. Or, how about Kazuo Hirai as a final boss with specials moves like RIDGE RACER and the 599 US Dollars finisher?